The present invention relates to a multi-layer dressing for wounds which provides for an initial period of wound hypoxia followed by oxygen availability to the wound, without disturbing the covering immediately in contact with the wound.
As understanding of the healing process has progressed, various theories have been advanced on the most advantageous way to treat wounds to promote healing. For many years, it was generally believed the wounds required atmospheric oxygen to aid epithelial resurfacing and so oxygen permeable wound dressings were used. Subsequently, however, it has been reported that oxygen-free or hypoxic conditions are either as good as, or preferable to aerobic conditions for the promotion of healing.
Alvarez et al. compared the effects of oxygen permeable and oxygen impermeable occlusive dressings on collagen synthesis and re-epithelialization. Infections in Surgery, March, 1984, pages 173-181. They found that occlusive dressings, and not the presence or absence of oxygen, led to improvement in both collagen synthesis and re-epithelialization.
Knighton et al. have reported that macrophage mediated angiogenesis is promoted by hypoxic conditions, and that, at least to the extent that new capillary growth is required, hypoxia is preferably maintained throughout most of the healing process. Allowing oxygen to contact the wound was found to slow angiogenesis unless capillary regeneration had proceeded to a point where more than 80% of the wound space had been filed. In that case, angiogenesis proceeded at the same rate, regardless of the atmospheric oxygen tension within the wound.